One-way Audio following IP Address Change

[robo764]

I've recently inherited a new network as part of beginning a new job.  Historically, my exposure to voice is pretty limited.  Without getting into the details of what lead to it, as it's not relevant, after performing a reset on an 8851, the phone grabbed a new IP address DHCP.  Later, I found out that, since the new DHCP assignment, the user had been experiencing one-way audio (callers could hear the user, but the user could not hear the callers).  There was nothing in the work I'd done that could have caused this, and I soon found out, from others that had been here longer, that this is something that has popped up from time to time. It's apparently so infrequent and intermittent, that it's never been a priority.  They have historically resolved the issue by replacing the phone. 

The phone and the CUCM are both at the same physical location, with only SVI between them.  The phone and all the other phones are on the same VLAN, many on the same switch.  There are over 200 phones registered that are not having any issues. I was able to find out that a phone in our IT Lab had the same issue (but was never replaced).  I was able to easily resolve the issue by deleting its DHCP lease, and creating a bogus DHCP reservation so the phone would be forced to grab a new IP.  Once it had a new IP, everything worked fine. I did the same with the user, and their issue was resolved as well.  I then, changed the second bogus DHCP reservation such that the IP Lab (Test) phone would get the user's OLD IP address, and the problem presented again.  I understand that one-way audio is almost always caused by routing issues, but with the nature and symptoms of this, it almost seems like there's something cached somewhere that's affecting only certain IPs.  The only thing I've experienced, in the past, that was similar was an issue with cached DNS entries needing to be manually cleared, but that was complete broken routing, not something like this. 

Anyway, even though it's not at the top of my priority list, I'd still like to understand what's causing this (especially if it's a routing issue that I'm not aware of). I'm still trying to do some research on the side, but has anyone come across a situation like this?  I'm also not sure what would be useful, so I just attached screenshots of call stats and diagram from the affected phones.

[Nithin Eluvathingal]

One-way audio issues are almost always (100% of the time) due to network problems. Verify the connectivity from the caller’s phone IP to the user’s phone IP. There might not be connectivity, but there could be connectivity from the user’s phone to the caller, which is why the caller can hear your voice.

You can quickly check if you are receiving packets from the phone settings. For the 8800 model, navigate to admin settings, then status, then call status. If you don’t see any RX packets, it means you are not receiving audio packets from the caller.

[robo764]

Thanks for the response.  As you can see in the attached files, I've already determined that the affected phone isn't seeing RX packets. I'm still trying to figure out the routing issue, but it's made trickier by its nature. Like I said, I'm trying to figure out why this one-way audio issue (routing, or otherwise) seems to only impact certain IP addresses that are within the same VLAN of all of the other phones. If the phone gets a different IP, it works fine.  If I move a working phone to that IP, it gets one-way audio. I understand it as a routing issue, I'm just unclear as to why it's only affecting certain IPs within the VLAN.

[robo764 · Accepted solution]

In this particular case, the issue seems to be with a couple of old Cisco ATA 191s.  They were no longer in use, but were somehow being forwarded traffic that should have been sent to phones.  There were two of them, which would correspond to the two phones that were having the issue.  What's strange about it, is that even after moving the phones to a different IP address, the issue would eventually follow the phone.  Power-cycling one of the ATAs resolve the issue of that phone/ATA, but I was honestly unable to tell why it was happening in the first place.  In the interest of resolving the issue, I just removed the ATAs from the network, but it still bugs me that can't wrap my brain around it.  I'm not even sure what I would be looking for.  The devices weren't ARPing, and from everything I could tell, didn't have any type of IP address.  The only traffic on their ports was broadcast traffic and the misdirected SIP.  In any event, the only clue I ever found was in the packet captures from the phone that showed the traffic going to the wrong layer2 address.  

[jgauchan]

Once way traffic/ rings and no voice ,normally happens, if you have not enabled port forwarding that is required by the phone system.

From my past experice working in small business- phone will ring but when you answer no voice or one way traffic.If you have a physical PBX on site that site needs to have all the range of port that is required pointing to the PBX system.